Recently, cushioning materials or spacers for packaging, made of a reusable sheet such as corrugated cardboard sheet or the like, have been proposed as substitutes for cushioning materials of styrene foam, which cannot be recycled or reused and adversely affect the life environment when discarded, as described in, for example, Japanese Patent Application laid-open No. H4-267769.
The cushioning material disclosed in the aforementioned Patent Application is constructed so as to support and protect the corners of an article when packed in a case, and every part thereof is composed of stacked (layered) corrugated cardboard.
When every part of a cushioning material is composed of stacked corrugated cardboard like this, the structure becomes simple but the bulk density (weight per unit volume) thereof increases and the cost becomes high.
To solve these problems, a cushioning material for packaging which uses a square cylindrical hollow body made of corrugated cardboard has been proposed, for example, in Japanese Patent Application laid-open No. H8-58842.
The cushioning material for packaging described in the above-mentioned Official Gazette Publication consists of a hollow body 6 having a square cross section, as shown in FIGS. 85 and 86, where parallel cuts 60, 61 are formed on both side portions so as to intersect at right angle with one edge of the body and a cut portion is formed on the edge between these cuts 60, 61 so as to form a plurality of symmetrical recesses 62 and protrusions 63. On two sides of the body 6 sandwiching the edge, flaps 66, 67 are made by forming folding lines 64, 66 extending between the ends of the cuts 60, 61 and a recess portion 60a is formed by folding the flaps 66, 67 inside and interlocking the aforementioned recesses 62 and protrusions 63 with each other.
The subject article is packed into a case with opposing edges of the article guided and supported by the recess portion 60a of this cushioning material.
Alternatively, as shown in FIG. 86, a pair of the bodies 6, 6 are united so that the recesses 60a, 60a are arranged in parallel to form a grooved recess 60a, 60a. The edges of the article 4 are guided and supported by the recess 60a, 60a and in this state the article 4 is packed in a case (not shown in FIG. 86).
Although the cushioning material for packaging disclosed in the above-mentioned Japanese Patent Application laid-open No. H8-58842 has a small bulk density as a whole and a simple structure, since it mainly consists of the hollow body 6, it has the following problems.
First, since the body has a square cross section and only a single hollow, it is liable to deform until a part of the article 4 is put into the recess 60a and packed in a case, which restricts movement of each body 6. This makes packaging difficult when the article 4 is packed into the case together with the cushioning material.
A second problem is that the bottom flaps 67 are weak, since, in the state shown in FIG. 86, the side of each bottom flap 67, 67 is connected to the side wall flap 66, 66 only by interlocking of a plurality of recess-protrusion portions 62, 63 and the weight of the article rests mainly on a central leg portion 68 of the bottom of the groove. Accordingly, only a very light article can be packaged.